Trouble with a complex, multi-conditional % Complete formula

This one is a doozy and I am a bit at a loss. Any help as to a single formula solution that results in a % Complete for each row would be so incredibly helpful!

Fact 1: For every row, Column G will have values "ISP & OSP - PRC" or "OSP Only - PRC" or "ISP Only - PRC"

Fact 2: If a row has a value of "ISP & OSP - PRC" in Column G, relevant columns that may have project milestone dates are: J, M, V, Y, AB, AE, AH, AK, AN, AQ, & AT

Fact 3: If a row has a value of "OSP Only - PRC" in Column G, relevant columns that may have project milestone dates are: J, M, Y, AE, AK, & AT

Fact 4: If a row has a value of "ISP Only - PRC" in Column G, relevant columns that may have project milestone dates are: J, M, V, AB, AH, AK, AN, AQ, & AT

Based on whichever of the three possible project type values that appears in Column G, I need a nested "OR" formula or something to that effect that will: count however many non-blank values appear in the appropriate columns for that project type (see Facts 2 through 4 above), and divide that by the total # of possible columns for that project type to get a % Project Complete figure.

attach an example pls.

Awesome. I modified it ever so slightly but COUNTA was the right solution to use within a nested IF formula. Thank you so much.

=IF(LEFT($F6,5)="isp &",COUNTA($J6,$M6,$V6,$Y6,$AB6,$AE6,$AH6,$AK6,$AN6,$AQ6,$AT6)/11,IF(LEFT($F6,5)="isp o",COUNTA($J6,$M6,$V6,$AB6,$AH6,$AK6,$AN6,$AQ6,$AT6)/9,COUNTA($J6,$M6,$Y6,$AE6,$AK6,$AT6)/6))